1. Field of the Invention
The present invention relates to a gas laser and particularly relates to a gas laser using a laser gas medium while circulating and purifying the laser gas medium.
In this specification, the concept "solidification" means a state in which gas molecules lose kinetic energy thereof on a surface to become solid on the surface. The concept "adsorption" means a state in which gas molecules attached to a surface have kinetic energy corresponding to the temperature of the surface so that the gas molecules are being attached under the balance between a desorbing force and an attaching force. Accordingly, solidified gas molecules are not replaced by others but adsorbed gas molecules are replaced by gas molecules having a stronger adsorbing force.
2. Description of the Related Art
Although a description will be set forth, by way of example, of the case where the present invention is applied to a KrF excimer laser, the invention is not limited to such KrF excimer laser. For example, the invention may be applied to a ArF excimer laser and the like.
A KrF excimer laser is operated in a manner so that a mixture of gas of about 95-99% of Ne, about 1-5% of Kr and about 0.1-0.5% of F.sub.2 is contained as a laser gas medium in a laser tube, which is made of metal, glass, plastics, ceramics or the like, and has mirrors disposed at the opposite ends of the laser tube, and light emission is caused in the laser gas medium through electric discharge to thereby cause resonance.
In general, a fluorine gas is strong in reactivity and, in particular, fluorine gas excited by electric discharge or other excitation means is so strong in reactivity that a reaction between the fluorine gas and constituent materials of the laser vessel is caused by the electric discharge. This can generate a level of impurities in the laser gas which causes the laser output from the KrF excimer laser to decrease as the number of discharge pulses increases due to the presence of these impurities.